Inductive tuning system



June 1, 19370 w. J. POLYBORQFF 299827595 I INDUCTIVE' TUNING SYSTEM Original File d April 22, 1933 2 Sheets-Sheet l INVENTOR, WLAD/M/EJ Panacea/= ATTORNEY.

June 1, 1937. w. J. POLYDOROFF 7 2,082,595

INDUCTIVE TUNING SYSTEM Original Filed April 22, 1933 2 Sheets-Sheet 2 WLAD/M/R].

ATTORNEY.

atented June 1, 1937 UNITED STATES 2,082,595 INDUCTIVE TUNING srs'rsiu Wladimir J. Polydorofi,

Chicago, Ill, assignor to Johnson Laboratories, Inc., Chicago, lit, a corporation of Illinois Original application April 22, rest, Serial No.

Divided and this application November 28, 1934, Serial No. 755,096. in Germany December 16, 1933 6 Claims.

The invention relates to radio receiving app ratus in which compressed magnetic cores are utilized as the tuning means. In such apparatus, the magnetic cores are arranged to be relatively movable with respect to the inductance coils, and the variation of the inductance, which produces the variable tuning, is brought about by varying the effective permeability of the space surrounding the coils. It is therefore convenm iently called "permeability tuning to distinguish it from other methods of inductance variation, and from methods in which the capacity is varied.

The several comminuted compressed magnetic cores and inductance devices which are described in this specification are disclosed in my co-pendmg applications No. 523,112, for Magnetic core material, Patent No. 1,982,689, issued December 4, 1934; No. 535,606, for improvements in highfrequency inductance devices, and No. 609,159,

for Improvements in variable inductance devices, Patent No. 2,005,203, issued June 18, 1935,

and hence no claims covering such improvements per se are herein included.

In permeability-tuned systems containing several tuned circuits, and intended to be tuned by a single control handle, there arises the problem of so designing and constructing the tuning unit that all of the circuits will be tuned very closely to the same frequency for each setting of the single control. This is accomplished partly by designing and" constructing the magnetic cores and the inductance coils so that they will be closely alike, partly by providing a mechanism which will insure that the cores (or the coils) will move in unison, and partly by providing adjusting means, so that any unavoidable discrepancies in the cores, the coils, or the operating mechanism, can be compensated for.

Adjusting means to correct for errors of alignment are shown in Figs. 1, 2, 3 and 6 and are I described in detail and claimed in my co-pending application, Serial Number 667,368, filed April 22, 1933, of which the present application is a division.

A principal object of my present invention is pie provision of switching means by which a receiving apparatus of the permeability-tuned type may be made to satisfactorily cover a much wider band of frequencies than would be conveniently possible by the variation of inductance alone. Other objects of the invention, and advantages secured by its employment, will also appear from what follows.

My present invention, therefore, contemplates that reasonable care will be taken to make the inductances alike, and that the cores, manufactured in accordance with my co-pending application, will also be closely alike. I then provide, in the present invention, in addition to mechanism for producing the necessary motion in unison of the several cores (or coils), the switching means hereinafter more fully described.

The invention will be better understood if reference is made to the accompanying drawings, which are illustrative of preferred embodiments, and wherein- Figure l is a plan view of an assembly of several high-frequency devices, in one unit, parts being broken away to reveal subjacent elements;

Figure 2 is a sectional view of said unit taken on the line 2-2 of Figure 1;

Figure 3 shows certain modifications of the tuning elements;

Figure 4 shows diagrammatically a receiving circuit employing one of the new high-frequency units;

Figure 5 shows switching means for altering the electrical constants of the circuits; and

Figures 6 and '7 show modifications of the highfrequency device.

The unit disclosed in Figures 1 and 2 has four shielded variable inductance devices arranged to operate simultaneously. This unit has a foundation plate i that is provided with flanges 2 to which rectangular shields 3 are removably secured by friction or by other means, and with ribs 2a which serve as mountings for removable semi-adjustable condensers 4. A perforated lug la rising from an edge of said plate, enables the unit to be connected with a suitable support.

Said foundation plate I also is provided with hexagonal tubular thimbles 5 through each of which extends a longitudinally movable screwthreaded rod 6 which terminates outside of the foundation plate 1, where it is provided with an adjusting nut l. Fixed to the inner end of each of said rods 6, is a coil form 8 having a hexagonal cavity 9 into which the hexagonal thimble 5 extends, the depth of this cavity being such as to permit said coil form to move longitudinally relatively to said thimble, but without disengagement therewith, said coil form, while thus moving, being prevented from rotating by its hexagonal engagement with said thimble. A helical spring I0 is disposed between said foundation plate I and each of said coil forms 8, in order to maintain said coil forms in their adjusted positions.

uide tubes 2i are once coil I3. The mechanism just described constitutes means for adjusting the positions of each of the coils I3 with reference to the cores 34, 39.

Said foundation plate I, furthermore, is provided with tubular sockets I4 for guide rods I5 which are parts of the mechanism for relative motion in unison between the several coils and cores of the unit.

The flanges 2, the hexagonal tubular thimble 5, and the tubular sockets I4, may be made integral with the plate I, as by die casting, or may be separately produced and secured to said plate in any suitable manner.

Associated with and movable toward and from said foundation plate I, is a core carrier IE, to which an actuating rod I9 is attached, said rod being in frictional engagement with a shaft 24. Said carrier I6 has holes 20 in which the ends of fixedly secured. The guide rods I5, carried by the foundation plate I, telescope with and accurately fit these guide tubes.

Carried by the aforesaid core carrier I B, are magnetic cores 56. These magnetic cores cooperate with the inductance coils I3 in such a way as to vary the effective permeability of the space surrounding the coils. Each magnetic core has a shell 34 having, in the head 36, an internallythreaded bushing 31 through which ,a screwthreaded rod 38 extends, and in which said rod is longitudinally adjustable.

Said core also includes a plug 39 into which is moulded the inner end oi said rod 38. The shell 34 may be spaced from the core carrier it, by an insulating washer 40 to exclude undesired infiuences of the metal core carrier on the core, and to leave room for a lock nut M which engages the screw threads of said rod 38, and, by contact with the head 36 of the shell 34, locks said plug 39 any one of its chosen positions.

The aforesaid construction allows both the plug 39 and the shell 34 to be made separately and assembled by simply screwing the rod 33 into the bushing 31 of the outer shell, and then tightening the nut 4i until it locks said parts together.

Each 01 the condensers is desirably disposed within one of the shields 3, whereby individual circuits are shielded from external influences and from each other. Hence, the problem of shielding inter-connecting wires between different parts of the same circuit is eliminated. The shields have holes 3a ail'ording access to the adjusting vice, consisting.

screws 54.

In some cases it is desirable to have two values of capacity in each circuit, as shown in Figure 3.

Figure 3 shows two condensers 4a, 4b, having different capacity values and mounted on ribs 2a.

The plug or the magnetic core and the coil I3a may, as shown in Figure 3, be cylindrical, and said coil may be bank wound, with several layers of wire.

In my co-pending applications No. 535,606 and No. 809,159, an improved variable inductance dei'or example, 01' a core 34, 39, a 0011 I3 and shield 3, is adequately described, and it is there pointed out that such a device is capable of maintaining a substantially constant ratio between the inductance and the radio-frequency resistance. This property is secured by the appropriate design and construction of the core and by so designing the coil that the inductance-toresistance ratio of the coil itself will have any desired value.

The selectance (expressed-as the width or the resonance curve at half amplitude) 01' the coil II tuning range, and

oi Figure 2 at 1500 k. c., with the core removed. will be approximately 22 k. c. With the improved core inserted into the coil, the selectance will be 18 k. c. at a frequency of 550 k. 0. By giving the core a factor of merit better than the inductancelac-resistance ratio of the coil, although the uniiormity of performance is somewhat impaired, the average properties of the circuit throughout the tuning range are improved. This is especially valuable in the case of a large inductance coil, bank wound.

The coil 14 of Figure 6 is intended for very high amplification or for operation in more than one has approximately twice as many turns as the coil I3 of Figure 2. The winding is of so-called Litz wire and is bank-wound. The inductance-to-resistance ratio of this coil is of the order of x10 at 1500 it. c.

Using a core whose factor of merit is 20 l0-", the inductance-to-resistance ratio of the combination at L50 k. c. is of the order of lilxlil and the selectance of the system varies from 42 to 30 k. c. Using the same coil M to tune from 500 k. c. to k. c., it has an inductance-to-reslstance ratio of the order of 40 10* bllil k. c., and of the order of 45 l0- at 180 c. Cline selectance of the circuit in this new band of frequencies is of the order of 8 k. 0. Thus, a considerable change in the selective properties of the circuits occurs if the same variable inductance idler/ice is used for two different bands of frequenoie Under normal conditions'o tion, for every operating ir within the range of adjustability, there is a corresponding position of the cores relative to th; a they produce an effective pe the coils such as to tune it that frequency.

It is possible, however, to the ratio at any desired frequency by the expedient of in rting the cores further into the coils to produce a higher effective permeability and thereiore a higher effective inductance, but, at the same time, ire-tuning to the desired frequency by readjusting the values of the capacities. the inductance-to-resistance ratio can be made considerably less than it would otherwise be, with a resultant decrease in the selectivity, which corresponds to a broadening of the selectivity curve. As is well known, the fidelity of radio circuits is determined by the sharpness of the resonance curves. The sharper the curves are, the more they discriminate against the higher modulation frequencies of the signal.

.The expedient just described, vides a simple method of broadening the selectivity and improving the fidelity of such circuits at will. For example, when it is desired to obtain maximum discrimination between signals, the circuits are tuned in the usual manner by moving the cores in accordance with the initial adjustments. When it is desired to improve the fidelity for a particular signal, a smaller capacity may be employed in each 01 the circuits and the cores moved further into the coils to again tune the several circuits to the desired signal.

Figures 4 and 5 show an arrangement for a radio receiving apparatus, in which a capacity switching arrangement is employed. This may be done to control the fidelity in the receiver, as just described, or it may be employed to produce an arrangement which can be tuned over two or more diii'erent'ranges of frequency. The variable inductances include coils I3 and com 58 which. with the capacities 51, form resonant circuits argo and opera By this expedient,

therefore, pro- Iii) ranged in cascade with the thermionic amplifiers 58. The signal received on the antenna 59 is fed to the first tuned circuit through a-capacity 62. Between the two thermionic amplifiers two resonant circuits may be capacitively coupled through either of the capacities 63, 64, or both. The plate circuit of the second thermionic amplifier is connected through a capacity 65 and a grid leak 86 with the detector amplifier 61, which is of the diode-triode type. This detector amplifier supplies audible signal for the output amplifier 68, and also supplies automatic volume control bias regulation to the high-frequency thermionic amplifiers 58.

When the switches 69 are in the position shown in Figure 4, all the circuits are responsive to the high-frequency band of the receiver, say 550 to 1500 k. c., with the antenna coupled through the condenser 62, and the bi-selector coupled through the capacity 56. When all the switches 69 are turned to the left, the capacities 51b, 57c, 51d and 51e are added to the circuits and the antenna coupling capacity is increased by the addition of condenser 51a, and the bi-selector coupling is also increased by the addition of condenser 63, thus changing the circuit constants so that the receiver will tune over a lower frequency band.

The switching may be conveniently accomplished by a two-way switch, such for example as that shown in Figure 5, which may be mounted on the back plate i of Figures 1 and 2. The I switch consists of a drum 10 made of insulating material and rotating through an angle of 90 degrees on a grounded metal shaft 11. On the drum I there are conductive inlays 12, some of which are connected to the grounded shaft 1|. The position of the switch shown in Figure 5 corresponds to the condition in Figure 4 when all the switches 69 are thrown to the left.

As has been pointed out, the same variable inductance device, when designed for two operating frequency ranges, will exhibit different selectivity and different gain in the two frequency ranges. To compensate for thedifierence in the two characteristics, the switch can be arranged to provide weaker coupling of the antenna to the first tuned circuit, and weaker coupling of the two circuits in the bi-selector, for the high-frequency range. The couplings are then automatically increased when the lower frequency range is in use.

Another method of securing operation in two frequency ranges, is indicated in Figure 6, where two separate coils 13 and 14 are arranged to be acted upon by the core or cores 56. The coil 13 is similar to the coil I3 of Figure 2 and is designed ---to operate over a range of frequencies from 550 to 1500 k. c., with a suitable condenser. The coil 15 is bank-wound to cover a new range of frequencies, such as from 180 to 500k. c., either with the same condenser or with a suitable additional capacity.

The core 56, or a group of similar cores, may be arranged to be moved laterally so as to engage with either set of coils. In an alternative arrangement, the coils may be arranged to move laterally, leaving the cores movable only in the original translatory manner.

It is also possible to mount the several coils for a particular frequency range on a plate i5, as shown in Figure 7, so arranged that the entire group of coils may be removed and replaced by a second group of coils designed to cover a different frequency band.

Having thus described my invention, what I claim is:

i. A multi-range system for a radio receiver including a plurality of tuned circuits each having inductance and capacitance, magnetic cores associated with, said inductances, tuning means for producing simultaneous movement ofsaid cores relatively to said inductances, coupling between at least two of said circuits, and switching means for altering said capacitances and said coupling, the values of said capacitances and of said coupling being so chosen that said system may be tuned over a plurality of frequency ranges and will have substantially the same performance characteristic in each of said ranges.

2. A multi-range system for a radio receiver including an antenna circuit and a plurality of tuned circuits each having inductance and capacitance, magnetic cores associated with said inductances, tuning means for producing simultaneous movement of said cores relatively to said inductances, coupling between at least two oi said circuits, and switching means for altering said capacitances and said coupling, the values of said capacitances and of said coupling being so chosen that said system may be tuned over a plurality of frequency ranges and will have substantially the same performance characteristic in each of said ranges.

3. A tuning unit for a radio receiver including a pair of tuned radio-frequency circuits each having an inductance coil and a capacitance, unitary tuning means for simultaneously varying the effective inductance values of said coils, a coupling capacitance connected between said circuits, plural additiona capacitances and a multiple switch adapted to connect one of said 7 additional capacitances into each of said circuits and to connect another of said additional capacitances between said circuits.

4. A tuning unit for tuning a radio receiver 'over upper and lower frequency ranges, including a pair of tuned radio-frequency circuits each having an inductance coil and a capacitance, said inductance coils being bank wound to a value suitable for said upper and lower ranges, unitary means for simultaneously varying the inductance values of said coils, a coupling capacitance connected between said circuits, plural additional capacitances and a multiple switch adapted to connect one of said additional capacitances into each of said circuits and to connect another of said additional capacitances between said circuits, the value of said coupling capacitance being so chosen that said receiver will have substantially the same performance characteristic in said upper and lower ranges.

5. A system for operating a radio receiver over upper and lower frequency ranges having in combination a pair of coupled resonant circuits each 4 including an inductance and a capacitance, said inductances each being bank wound, means for increasing said inductance values to select desired signals in either of said ranges, a coupling capacitance connected between said circuits, plural additional capacitances and a multiple switch adapted to connect one of said additional capacitances into each of said circuits and to connect another of said additional capacitances between said circuits, the value of said coupling capacitance being so chosen that said receiver will have substantially the same response to signals in either of said ranges.

6. A system for operating a radio receiver over upper and lower frequency ranges having in combination a pair of coupled resonant circuits each including an inductance and a capacitance,

said inductances each being bank wound to a value suitable for said upper and lower ranges, means for increasing said inductance values to select desired signals in either of said ranges, a coupling capacitance connected between said circuits, plural additional capacitances and a multiple switch adapted to connect one of said additional capacitances into each of said circuits and to connect another of said capacitances between sald circuits.

WLADIMIR J. POLYDOROFF. 

